Butadiene is a raw material for butadiene rubbers, styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, ABS resins, and the like, and is one of the most important organic compounds in the chemical industry. Butadiene can be converted to adiponitrile, which is an intermediate for synthesis of nylon 66, chloroprene, which is a raw material for chloroprene rubber, or 1,4-butanediol, which is a raw material for polybutylene terephthalate. These polymer compounds produced using butadiene as a raw material are widely used for not only industrial goods such as automobile tires, electric wire coatings, and engineering plastics, but also daily necessaries such as clothing. Butadiene has been increasingly demanded year by year.
Butadiene is mainly produced by extraction separation from the C4 fraction generated during production of ethylene by a naphtha cracker. However, it is expected that, as the raw material of ethylene shifts to natural gas, shortage of supply of butadiene may occur in the future. In view of this, methods for producing butadiene using natural gas as a raw material have been studied in recent years. However, because of problems such as depletion of fossil resources in the future, global warming due to greenhouse gas emission, and the like, realization of sustainable butadiene production is increasingly demanded. Therefore, development of a method for producing butadiene from biomass resource-derived substances, which are renewable sources, is demanded.
2,3-Butanediol is a polyol used as a raw material for inks, perfumes, liquid crystals, insecticides, softening reagents, explosives, plasticizers, and the like. Industrially, 2,3-butanediol is produced by a method in which 2-butene oxide is hydrolyzed in an aqueous perchloric acid solution. On the other hand, since 2,3-butanediol can also be produced by microbial fermentation using as a raw material a monosaccharide such as glucose or xylose (Patent Document 1), it is a substance derivable from biomass resources. Thus, if production of butadiene by dehydration of 2,3-butanediol can be achieved, butadiene, and existing synthetic resins using butadiene as a raw material, can be replaced with biomass resource-derived substances.
It is known that dehydration of 2,3-butanediol can be carried out using an acid catalyst. For example, a method in which 2,3-butanediol is dehydrated by bringing the 2,3-butanediol into contact with Japanese acid clay has been disclosed (Non-patent Document 1). A method in which 2,3-butanediol is dehydrated by treatment in an aqueous sulfuric acid solution has also been disclosed (Non-patent Document 2). Further, a method in which 2,3-butanediol is dehydrated by bringing the 2,3-butanediol into contact with zeolite has been disclosed (Non-patent Document 3). However, the main product in these methods is methyl ethyl ketone rather than butadiene.
Methods in which butadiene is selectively produced by dehydration of 2,3-butanediol have been reported. Non-patent Document 4 discloses a method using a thorium oxide (ThO2) catalyst; Patent Document 2 discloses a method using a cesium oxide-carrying silica catalyst; and Patent Document 3 discloses a method using a hydroxyapatite-alumina composite catalyst.
Butadiene can also be produced by dehydration of 1,3-butanediol. Patent Document 4 discloses a method using a catalyst composed of a mixture of sodium dihydrogen phosphate (NaH2PO4), calcium monohydrogen phosphate (CaHPO4), phosphoric acid (H3PO4), and butyl amine-phosphoric acid (BuNH2.H3PO4), wherein the selectivity of butadiene is reported to be 77%.